Power takeoffs for motor vehicles, are designed to utilize the power train of the motor vehicle to drive auxiliary mechanisms either mounted on or carried by the vehicle. Examples of such auxiliary equipment are winches, hydraulic lifts, etc. Power takeoffs for manual transmissions are very common in the art. Power takeoffs adaptable for automatic transmissions are less prevalent and usually involve power takeoff from a gear inside the automatic transmission or from the fan belt section of the engine. In view of the complicated nature of modern motor vehicle engines, the large number of auxiliary elements attached to such engines and the relatively small space within the engine compartment, attaching power takeoff units to the fan belt section of a motor vehicle is difficult from the standpoint of the lack of suitable space and the complications involved in acquiring driving connection to a belt driven by the engine. Power takeoffs from the gears in an automatic transmission suffer structural deficiencies that limit the use of power developed by the transmission.
Power takeoffs for vehicles with manual transmissions commonly are designed to be interposed within the drive train of the motor vehicle between the transmission and the differential. These takeoff units are notoriously complicated and bulky. In U.S. Pat. No. 2,494,111, there is proposed a power takeoff structure that is indicated to be relatively small and short so as to be conveniently mounted in the restricted space of the motor vehicle. The inventor in this patent, in order to achieve the desired results, was required to design a power takeoff element that was concentric with the driven input shaft and therefore requiring the design, manufacture and assembly of complicated positioning apparatus for maintaining the relative rotatable and nonrotatable postures of the power takeoff element relative to the constantly driven input drive shaft. This design further requires the use of a relatively complicated and expensive supporting sleeve for the power takeoff element. It will be clear hereinafter that the present invention provides a much more simple, effective power takeoff mechanism that is less expensive to manufacture, assemble and repair.
In like manner, U.S. Pat. No. 1,258,883 discloses a power transmission mechanism including a power takeoff element that is exceptionally bulky, complicated and therefore expensive to manufacture and to maintain. In addition, the power transmission path through the various elements of the unit disclosed in this patent follows tortuous paths that can result in deleterious torque forces and premature maintenance requirements.
Other prior power takeoff units provide for constant engagement of the power takeoff element such as in U.S. Pat. No. 3,049,929 with only selective engagement or disengagement of the motor vehicle drive shaft. Such units require additional control mechanisms for adjusting the output of the power takeoff unit in the course of its operation of the device that is to be powered by the unit.